Boosting aerobic heterotrophic biomass productivity and quality on brewery effluents: Impact of different high-rate processes, biomass age and anaerobic acidification. undefined

The increasing demand for animal-derived protein pushes on the intensification of soybean and fish meal feed production, raising concerns about the escalation of environmental problems and food security. Alternative protein sources, such as microbial protein (MP), may be an attractive solution to the increasing scarcity of feed, especially when combined with resource recovery. Among the MP, aerobic heterotrophic bacteria (AHB) emerge as strong candidate due to their high nutritional quality and growth on secondary resources. To maximize AHB production, high-rate activated sludge (HRAS) is envisaged as a core technology. Three parameters were selected to test HRAS performance treating synthetic brewery wastewater: i) reactor configuration, by comparing a high-rate conventional activated sludge (HiCAS) with high-rate contact stabilisation (HiCS); ii) three solids retention times (SRT), 0.25, 0.50 and 1.00 d; iii) and type of substrate (raw and fermented) to verify the necessity of pre-fermentation prior to AHB production. These parameters are known to affect microbial community composition which can have an impact on biomass productivity and quality. Within the same SRT and substrate, HiCAS and HiCS obtained similar biomass (between 8.0-4.4 g TSS/L/d) and protein productivities (between 3.2–1.9 g protein/L/d), although HiCAS had greater chemical oxygen demand (COD) removal efficiencies, up to 98%. The reactors treating raw wastewater obtained a higher AHB productivity, reaching a maximum of 8 g TSS/L/d (HiCAS at SRT 0.50 d). AHB grown on fermented wastewater had a mean protein level of 45%, 6% more than those on raw wastewater (p=5.1E-5), notwithstanding comparable protein productivities. The AHB biomass from most of the treatments resulted in an essential amino acid (EAA) profile similar to fish meal, and above rainbow trout requirements, excluding the S-containing EAA. SRT was found to have the highest impact in the AHB community composition. The findings show that all high-rate technologies and tested substrates can be used to reach high AHB and protein productivities along with promising EAA profiles.